Isotopologues are molecules that differ only in their isotopic composition. Hydrogen-related isotopologues of normal or “light” water (H20) include “semi-heavy water” having a single deuterium isotope (HDO or IH2H0), “heavy water” with two deuterium isotopes (D20 or 2H20), tritiated water having a single tritium isotope (HTO or 3HOH) and “super-heavy water” (T20 or 3H20). For purposes of this disclosure, the term tritiated water will be used to refer to any water molecule in which one or both hydrogen atoms are replaced with a tritium isotope. Tritiated water is a byproduct of nuclear power generating stations.
Tritium is chemically represented as T or 3H and is a radioactive isotope of hydrogen. Tritium is most often produced in heavy water-moderated nuclear reactors. Relatively little tritiated water is produced. Nevertheless, cleaning tritiated water from the moderator may be desirable after several years of operation of the nuclear station to reduce the risk of tritiated water escaping to the environment. Very few facilities exist that can properly clean or separate tritiated water from a solution or mixture of tritiated water and normal water. The scarcity of facilities makes it necessary to transport relatively large volumes of contaminated water solution containing relatively small volumes of tritiated water across long distances to a location such as Ontario Power Generation's Tritiated Water Removal Facility. Ontario Power's facility can process up to 2.5 thousand tons (2,500 Mg) of contaminated heavy water per year, producing about 2.5 kg of tritiated water.
Tritiated water is produced in pressurized light water reactors as well. The prevalence is directly related to the use of Boron-10 as a chemical reactivity shim. A shim is used to convert high energy neutrons to thermal heat. The production of this isotope follows this reaction:5B10+0n1→[5B11]*→1H3+2(2He4).
The half-life of tritiated water is 12.4 years. This is troublesome because it is persistent enough to concentrate in the reactor water. Tritiated water causes no ill reactivity effects within the nuclear reactor, but it does provide a significant risk for contamination from small leaks. Tritium is chemically identical to hydrogen, so it readily bonds with OH as tritiated water (HTO), and can make organic bonds (OBT) easily. The HTO and the OBT are easily ingested by consuming contaminated organic or water-containing foodstuffs. As tritium is not a strong beta emitter, it is not dangerous externally, however, it is a radiation hazard when inhaled, ingested via food or water, or absorbed through the skin. In the form of tritiated water molecules, it can be absorbed through pores in the skin, leading to cell damage and an increased chance of cancer.
HTO has a short biological half life in the human body of 7 to 14 days which both reduces the total effects of single-incident ingestion and precludes long-term bioaccumulation of HTO from the environment. HTO does not accumulate in tissue.
Enrichment of tritiated water by removing the excess water and concentrating the tritiated water can significantly reduce the expense of transporting very low level contaminated materials to a cleaning facility. The available processes are not commercially attractive when starting with low concentrations of tritium as tritiated water because of the transportation costs. No low cost processes have been demonstrated for the concentration of tritiated water due to the fact that it has physical and chemical characteristics that are so similar to water that it precludes normal chemical or thermodynamic measures. These close similarities have previously made it difficult to define processes that will efficiently separate the tritiated water from water. Accordingly, the present disclosure provides improved methods, devices, and systems for separation of isotopologues, including the separation and concentrating of tritiated water, to enable more economical disposal.